1. Field of the Invention
The present invention relates to a torque-controllable screw with a knob which can control the torque when the screw is screwed and tightened. This application is based on patent application No. Hei 11-328768 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
There exists a screw which has a screw shaft in which a male screw is cut on one end thereof and a knob connected to the other end of thereof. The screw is used for fastening a SCSI type outer terminal connector or a SCSI type cable connector.
With this type of screw, little consideration is placed on the rotation direction, so that, if the screw is mainly designed for unfastening, the screw may slip toward a female screw for engaging the male screw, before the screw is fastened with necessary force. On the other hand, if the screw is mainly designed for fastening, the screw may slip when the screw is unfastened from the female screw. Thus, an object of the present invention is to provide a screw which can satisfactorily both fasten and unfasten.
A screw of the present invention comprises a screw shaft in which a male screw is cut on one end and a knob which is connected to the other end thereof. Furthermore, the screw shaft and the knob have a torque controller which rotates the screw shaft and the knob together until a rotating torque between the screw shaft and the knob reaches a predetermined level, and slips the knob toward the screw shaft if the rotating torque exceeds the predetermined level, while the knob is rotated along a direction for screwing the screw; and the torque controller also rotates the screw shaft and the knob together even if the rotating torque exceeds the predetermined level, while the knob is rotated along a direction for unscrewing the screw.
With this torque controller, the maximum level of the rotating torque along the direction for unscrewing the screw can be greater than that of the rotating torque along the direction for screwing the screw. Therefore, if the screw is mainly designed for fastening, the screw does not slip when the screw is unfastened. Thus, the screw can properly fasten and unfasten when used with simple structures.
It is preferable that the torque controller has claws on the outer surface of the screw shaft, and that each of the claws has a first inclined surface which contacts the knob at a relatively gentle angle when the knob is rotated along the direction for screwing the screw, and a second inclined surface which contacts the knob at a relatively sharp angle when the knob is rotated along the direction for unscrewing the screw.
With this torque controller, because the first inclined surface contacts the knob at a relatively gentle angle, the torque for getting over the claws is reduced when the knob is rotated along the direction for screwing the screw. Furthermore, because the second inclined surface contacts the knob at a relatively sharp angle, the torque for getting over the claws increases when the knob is rotated along the direction for screwing the screw. Therefore, if the screw is mainly designed for fastening, the screw does not slip when the screw is unfastened.
It is further preferable that the knob has projections on the inner circumferential surface of the knob, and each of the projections contacts the first inclined surface and elastically deform on the first inclined surface when the knob is rotated along the direction for screwing the screw with a rotating torque which exceeds the predetermined level.